[R] nls and discontinuous functions

[Peter Dalgaard]

Luis Orlindo Tedeschi wrote:
> Folks; I have looked for this subject extensively using all the resources I have available and could not find a solution; therefore I am sending you this email seeking for help. I need to solve a discontinuous nonlinear function, but R 2.6 keeps giving me an error. Below is a simple example:
>  
> f <- function (t,k,l,u) { r0<-346.1 x<-t-l if (x<0)  r0 else  (r0-u)*exp(-k*x)+u }prof1<-read.table("c:\\data.txt", header=TRUE)results<-nls(y1~f1(t,k,l,u), data=prof1, start=list(k=0.05, l=4, u=154))
>  
> Errors I am getting are: 
>  
>  
> Error in qr(.swts * attr(rhs, "gradient")) :   dims [product 3] do not match the length of object [10]In addition: Warning messages:1: In if (x < 0) r0 else (r0 - u) * exp(-k * x) + u :  the condition has length > 1 and only the first element will be used2: In if (x < 0) r0 else (r0 - u) * exp(-k * x) + u :  the condition has length > 1 and only the first element will be used3: In if (x < 0) r0 else (r0 - u) * exp(-k * x) + u :  the condition has length > 1 and only the first element will be used4: In if (x < 0) r0 else (r0 - u) * exp(-k * x) + u :  the condition has length > 1 and only the first element will be used5: In if (x < 0) r0 else (r0 - u) * exp(-k * x) + u :  the condition has length > 1 and only the first element will be used6: In .swts * attr(rhs, "gradient") :  longer object length is not a multiple of shorter object length
> Data file is this one
>  
>  
>     t    y1
> 1   0 346.12   3 343.13   6 327.44  12 280.95  18 242.76  24 228.67  36 193.48  48 174.29  72 164.810 96 152.0 
>  
>  
> Any help?
>  
>   
It would be easier to help if you could persuade your emailer not jumble
up you code....

However, I suspect that you need to look into the difference between if
and the ifelse() function.

    -pd

> Thanks a lot
>  
> Luis
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-- 
   O__  ---- Peter Dalgaard             Øster Farimagsgade 5, Entr.B
  c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
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